Charged particles accelerator



PHASEANGLE AT THE GUT/.ET 0F THE PHASEANGLE AT THE OUTLETOF THE ORD/,VARY S/NGLE TYPE FHASE PHASE BUNCH/N6 APPARATUS ACCORD/N6 T0 July 25, 1967 YAsuTsuGu TAKEDA ET AL 3,333,142

CHARGED PARTCLES CCELERATOR Filed March 19, 1963 3 Sheets-Sheet l PHASE SH/FTE? DUMMYLOAD Ff L f3 ,//7 n@ RA DIO FREOUE/VC Y ENERGY SOUHC E k HHIIHHHIII IIIHIIIIIIHIIII /L 7( numlujLlumuuumn July 25, 1967 YASUTSUGU TAKEDA 5T AL v 3,333,142

CHARGED PARTICLES ACCELERATOR Filed March 19, 1963 3 Sheets-Sheet 3 ELE C TRO/V GUN MAGNET/C FIELD United States Patent G 3,333,142 CHARGED PARTlCLES ACCELERATOR Yasutsugu Takeda, Nakano-ku, Tokyo-to, Yoichi Kaneiro and Ai-:iji Maeirawa, Hachioii-shi, Ryoka Sawada, Kitatarna-gun, Tokyo-to, Hiroshi Kimura, Kita-ku, Tolryoto, and Kunishige Kuroda, Euganei-shi, Japan, assignors to Kabushiki Kaisha Hitachi Seisakusho, Tokyo-to, Japan, a joint-stock company of Japan Filed Mar. 19, 1963, Ser. No. 266,429 Claims priority, application Japan, Mar. 22, 1952, 37/ 10,638 3 Claims. (Cl. 31S--5.39)

This invention relates to a charged particle accelerator. More particularly, it relates to an apparatus incorporating novel design features applied to a conventional two chamber velocity modulator type electron bunching apparatus wherein a much greater bunching effect is attained and which apparatus can be designed and manufactured much more easily and readily than a conventional traveling wave type velocity modulator apparatus.

lt is an object of the present invention to provide a construction whereby a circular corrugated wave guide tube as is most commonly employed as an electron beam accelerator in a linear type electron beam accelerator is accurately established in length in promoting smooth conversion of the phase velocity of the radio frequency wave throughout the tube length and for establishing the relative value of the mutual interaction between the radio frequency waves and electrons by elimination of mathematical proximations and exacting and time consuming laboratory experiments.

1t is another object to simplify the design and manufacture of an electron beam accelerator which will not be subject to factors of critical manufacturing tolerance and strict dimensional requirements.

A further object of the present invention is to promote a greater bunching of electrons substantially higher than 60% which is commonly available with conventional velocity modulating type phase :launching systems.

Still another object of the invention is to attain a bunching of electrons substantially higher than 75% within iOlir radian in a two chamber type velocity modulatingy phase bunching apparatus.

These and other objects will become apparent from a study of the specifications and drawings which are attached hereto and form a part hereof, and in which;

FIG. l shows a simplified form of an accelerator tube;

FIG. 2 is a schematic layout of the principal elements shown for purposes of explaining the functional theory;

FIG. 3 is a graph showing bunching of approximately 90% of the emitted electrons Within a phase angle proximity of O lfr rad.;

FIG. 4 is a graphical presentation of the bunching of emitted electrons in the case of an apparatus of the one chamber velocity modulating type;

FIG. 5 is a graphical presentation illustrating the bunching of electrons in the case of a two chamber velocity modulating type apparatus;

FIG. 6 is an example of execution of the apparatus of the present invention;

FIG. 1 is a graph depicting the calculated deductions of electrons developing several types of initial phases;

FIG. 8 is given for illustration showing the manner by which miniaturization of an apparatus can be accomplished by the location of a discriminator in top of the chamber in a typical velocity accelerator apparatus;

FIG. 9 shows a drift cavity in the shape of an arc illustrating a typical location of component parts of an apparatus or in solving problems of space.

Referring now to FIG. l which is a schematic diagram of a general electron accelerator device of linear type,

3,333,142 Patented July 25, 1967 electr-on 2 emitted from an electron gun 1 is hunched and accelerated by a bunching-accelerating device 4 which has been energized by high frequency power supplied from a high frequency source 3, and then it is further accelerated at the exit of the tube 4 to the order of 097-099 C (C is the light velocity). This accelerated electron is further accelerated substantially to the velocity of light iiux by a light Velocity accelerator tube 5, and thereafter it is taken out through an electron-permeating hermetic window 6 for use. The reference numerals 7 and 3 indicate, respectively, a phase shifter and high frequency dummy load.

Referring now to FIG. 2, a uniform electron beam 2 emitted from the electron gun 1 and accelerated at a uniform acceleration voltage Vo(kv.) and propelled at a velocity veo (m/sec.) is, under the influence of a radio frequency field voltage V1 sin wt(l v.), subjected to velocity modulation in its passage through the modulation gap G1 in the No. 1 chamber C1, the latter being pulsed through the terminal 9. After the electron beam had been subjected to velocity modulation, it drifts through the distance Il. It then passes under the inliuence of a radio frequency voltage V2 sin (wt-) through the modulation gap G2 in the No. 2 chamber C2 and is pulsed through terminal 1t). The electron beam thereby is again subjected to velocity modulation and, after being allowed to drift through the distance I2, it is introduced into a secondary stage (not shown) such as a light velocity accelerator. in the foregoing represents the phase angle relationship of the radio frequency phase in the chamber C1 and radio frequency phase in the chamber C2. The value of this phase angle may be appropriately selected by means of a phase shifter.

Before giving various relative equations with respect to the detection of two sets of bunching parameters and modulating voltage of respective resonant cavities, which are the most important features of this invention, general phase-bunching characteristics are presented below of the device as shown in FIG. 2 in the form of equations.

Now, if it is assumed that electrons pass through the gap G1 in No. l chamber C1 Within time t at a phase angle 0(6:wt), pass through the drift area (distance l1), and reach gap G2 in the No. 2 chamber C2 within time t1, the phase angle 61(01=wt1) may be expressed by the following equation;

l V t1 t i (T01- E 71117111); Sill cui) In the aboveall or the electron transit angle in No. l drift chamber i.e., distance l1- Bunching parameter for the No. l chamber vll-:Gap coupling coefficient for the No. l chamber gap Gl-the coefficient being a fixed constant normally less than but nearly equal to unity.

(wherein C is the light velocity) E=radio frequency field strength in the accelerator tube Elect-ron transit angle in `the No. 2 drift Area i.e., distance l2 Bunching parameter for the No. 2 chamber 112 Gap coupling coefficient for gap G2 in No` 2 chamber.

mVi A nzVz Accordingly, the foregoing had been applied to a conventional apparatus by assuming =01, setting up as relationship between 02 `and 01 and executing analysis only under the following conditions, ie.,

iogxao Logxzgao Y or ythe proximate point at which the transitting electron has velocity modulated in the No. l chamber would display a maximum value of the fundamental component of radio frequency current. However, the maximum expectable bunching of electrons with a i0.l7r rad. in apparatuses of presently known construction was found to be labout 75% of the total electron emission.

For the purpose of detecting such parameters, the invention takes the value of the buuching parameter X1 of the rst resonant cavity followed by a drift tube far greater than the value which has heretofore been considered optimum so as to improve actively the overall bunching characteristics of the device. In this case, since the operating gap voltage 171V1 within the resonant cavity is made suiciently low, Ithe length of the rst drift tube becomes long with the result that about 90% of electrons which have reached the second high frequency cavity is hunched within the phase sector of n*0.61r- +0.61r radian. On the other hand, the value of the bunching parameter X2 of the second resonant cavity followed -by a drift tube is selected at about half of that of the lbunching parameter X1. This selection of 4the values wouldV give an extremely good phase-bunching charac- -terist-ics only on electrons whichare injected in the vicinity of -0.61r to +0.61r radian. Furthermore, by making Vthe value of the operating gap voltage 2V-2 within the second resonant cavity suiciently larger than theoperating gap voltage 111V1, the influence of the rst cavity at this portion can be made Ithe least. And, as far `as various combinations of the values of X1, X2, ,11V1, and o72V2 can satisfy the equation named below which is given to meet the above-mentioned requirements, the optimum conditions can be secured.

In the present invention, however, it is taken that And V A=Mfu1 In accordance with the above, it has been found, as

shown in FIG. 3, that it is feasible to bunch 90% of the emitted electrons within r0.1# rad. proximity of the phase angle 02(01{02). This resultant yield is comparable to that attainable with conventional one chamber velocity modulating designs or two chamber velocity modulator apparatuses. When compared with graphs FIG. 4 and FIG. 5, it is readily apparent that Ithe bunching effectiveness is extremely great. As compared with the bunching effectiveness of a conventional travelling wave accelerator apparatus, it is deficient to the extent of about 5%, which deficiency, however, is -amply compensated for by the economies in design Iand manufacture afforded by the apparatus of the present invention. FIG. 5 shows the curve plotted for the case of:

Still further, in a high frequency amplifier tube utilizing an electron bunching function, it is a problem how much high frequency current component of a certain specific frequency exists in the electron beam, while, with respect to the electron bunching in `an accelerator become a problem. Only the number of electrons which can be accommodated within a certain phase width is open to question. Accordingly, the present invention provides an apparatus which affords extremely high performance, wherefore the instant .apparatus is an invaluable and advanced development. v Y

Referring to FIG. 6 which represents an example of practice of the present invention, electron beam 2 uniformly emitted from the electron gun 1 is subjected to velocity modulation by the modulator gap G1 in the portion of the No. 1 chamber C1 pulsated by the output of the radio frequency source 3'.

As stated above, the electron beam, which has been vvelocity modulated by the modulation gap G1, drifts in a distance l1 of the drift region, and thereafter is further subjected to velocity-modulation by the Vmodulation gap G2 of the second chamber C2. Thus, this second chamber C2 is excited by high frequency Waves induced from a part of the output for ythe above-mentioned radio frequency energy source 3', and this high frequency wave has a desired phase relationship with respect to high frequency which excites the first cavity. y

After travelling the distance l2 in the drift region, the electron beams are injected directly into the light velocity accelera-tor tube 11. The reference numerals 12 vand 12' denote phase shifters, 13 and 13' represent variable attenuators, and 20 indicates a directional coupler.

The following is an explanation of how Ithe charged particle stream thus phase-hunched will receive, without loss, the traveling wave form radio frequency excited in accelerator tube 11 and then will further be accelerated. 1 In general, the moti-on of electrons in a light velocity tube such as 11 is expressed by the following equations:

5 The normalized distance or the distance from the entrance of the yaccelerator tube normalized by the wave -length of the operating radio frequency.

A relative phase angle of the electrons in relation to the radio frequency e.E.)\ a 111.02 normalized radio frequency field strength in the accelervator tube of a general type as in the present invention, this does not E--radio frequency iield strength in the accelerator tube e=charged quanti-ty 0f electron m=mass of electron c=light velocity Ve=velocity of electrons =radio frequency wave length.

Referring to FIG. 7 representing the curve determined by calculations for several series of electrons producing an initial phase by substitution of a value for a=4.0, ,6e(0)=0.5 in Equations 4 and 5, it is found that the electrons ejected within an initial phase of i017 rad. in the No. 1 chamber trace a path confined within the shaded area, and, under the condition of 2 the phase A of the electrons will generally be confined between 80 .to 82 and continue to travel thereafter at an accelerated rate without any practical change in phase. D in the present instance is approximately unity `and represents the distance from the entrance of the accelerator 4tube or the point at which the phase of the transmitting electrons in the light accelerator tube approaches approximately 90. It is generally recognized that electrons -in respect to radio frequency phase acceleration are most eiciently -accelerated at A= 90. The achievable energy of electrons under this best condition according to the apparatus of the present invention is approximately 98.5-99% and is accompanied by only a narrow phase distribution. Consequently, the apparatus of the present invention provides an extremely eflicient means for accelerating electrons with a narrow accelerating energy distribution spectrum and allows, moreover, attainment of ysubstantially high energy values.

Now, if the output of an electron bunching means i.e., the electron beams from a phase buncher, is coupled directly to a light velocity accelerator tube as shown in FIG. 6, it will be found that the yacceleration eciency in the vicinity of the entrance of the accelerator tube Ogo will not be very high as compared with the portion corresponding to l because of the gradual change in the phase angle of the electrons as they travel from the vicinity of 0 to 90. This undesirable deficiency may, however, be remedied by preliminary 'acceleration of the electrons to the velocity of light and also by aligning the electrons from the start in the vicinity -of a phase angle of 90 in relation -to the radio frequency wave `at the mouth of the light velocity accelerator tube. With this preliminary measure taken, and electrons injected into the light velocity accelerator tube, it is possible to attain Ia considerably higher acceleration eliciency. In illustration of the foregoing approach, reference is made to FIG. l wherein the values of a for the accelerator tube S and its length are equal, respectively, to the corres-ponding parts shown in FIG. 6, the energy of the electron beam at the terminal of the accelerator tube will have a maximum value of mev. with an energy Width of approximately 2%. Now, Were Van attempt to be made to produce an apparatus patterned .after the construction in FIG. 1 to match the performance of an apparatus `conforming to the construction shown in FIG. 6, it would be found that the electron bunching accelerator tube would have to apply an average energy of about 2 mev. and limit the energy distribution to an extremely low value of less than 0.04 mev. Experience has shown that the design and manufacture of an electron bunching accelerator tube with an `allowable energy width of such small value is extremely difficult. Moreover, and from a practical standpoint, no established method is known to reasonably permit the construction of an electron bunching accelerator of such rigid specifications which would provide predetermined phase bunching characteristics as well as increased electron energy output and width. As previously explained, an apparatus of the type shown in FIG. 1 would necessitate painstaking laboratory experiments. Needless to state, its design and manufacture would be extremely troublesome, diicult and time consuming. Consequently, the apparatus of the present invention, in contrast to conventional apparatus as typified in FIG. 1, is characterized by its feature of extreme ease in design and manufacture.

In the conventional electron bunching accelerator tubes, it had been necessary to carry out acceleration and phase-bunching simultaneously. However, both acceleration and bunching cannot usually be done simul- -taneously by these prior apparatus. That is, from the point of the bunching effect, when the bore of the wall of the travelling wave-accelerator tube, for example, is made gradually narrower -along its distance in order to satisfy the relationship of dat) d the acceleration etect is inevitably impaired. Accordingly, when attempting to improve the impairment of the acceleration effect by changing the bore of the wall, more complications in design and manufacture result. The apparatus of 4the present invention, however, is concerned principally with the acceleration phase as explained above, and it permits satisfaction of the equation dat) di 0 Therefore, in the instant apparatus, there can be provided an accelerator tube lof relatively simple design which performs acceleration only close to the light velocity between the velocity modulation type bunching part and the light velocity accelerator with the result that the apparatus has the advantage of relatively simple design and manufacture.

Further, in explaining the present invention and on the basis of the example of execution as typified in FIG. 3, the apparatus makes it possible to bunch ofthe total electron emissions within t0.11r radian. Although the iigure shows only the right side of the graph, it is exactly symmetrical with the left side with respect to the origin. As has already been explained, FIGS. 4 and 5 are the characteristic curves of the velocity-modulation type phase-bunching -apparatus according to prior art. The balance of electrons deviates substantially from the specication energy value and, as such, they appear as a noise component. This noise component can, however, be removed by means of an energy discriminator provided with .a slit or an analyzing magnet positioned before the light velocity accelerator tube or at its extremity or, as later described, by the provision of a suitable means for phase discrimination of yany electrons falling outside of the desired phase `angle range before the electron beam is introduced into the light velocity accelerator tube.

-In the apparatus of the present invention, the provision of discriminator means 14 in FIG. 8 as noted in the foregoing paragraph, is made in the extra space between the chambers No. 1 and No. 2, the extra space resulting from the adoption of a greater bunching parameter X1 than in normal practice for the No. 1 chamber according to the present invention. This provision contributes to the miniaturization of the apparatus.

The discriminator means above mentioned is identified in FIG. 8 by the numeral 14. It is seen that the means is an integrated system composed, as an example of illustration, of a radio frequency modulator 15, a discriminator 16 and a beam focusing means 17, the composite group forming a resonant chamber energized by a part of the radio frequency pulse output through the medium, for instance of an attenuator means 13 and a phase shifter 12".

The operation of this discriminator is now described as follows. A part of the output from a radio frequency pulsator is appropriately phase adjusted by the phase adjustor means 12" and introduced to the radio frequency modulator 15 where the phase adjusted energy serves to deect the path of travel of electrons emitted from an electron gun from its original orbit (Z axis) to a course of intersection or in a direction at right angle (Y axis). Consequently, electrons passing through the radio frequency modulator ladvance along the X axis at differing slope angls (at an angle proportional to dY/dZ) in terms Vof time and depending on the variation in amplitude of the radio frequency subject to modulation. If now a discriminator provided with a predetermined slit width is positioned in coincidence with Y axis at a certain point from the radio frequency modulator 15, only those electron beams of a predetermined phase range in yone cycle of the radio frequency subject to modulation will pass through the above noted slit thus prohibiting the passage of undesirable electron beams. Furthermore, the electron `beams passing through the above stated slit can be induced to resume their path of travel along the Z axis by means of the beam focuser 17 forming a part of the electron lens system. Accordingly, it is readily apparent that the apparatus of the present invention embodying a functional means for input phase discrimination of charged particles provides the means for first elimination of those electron beams having an input phase angle of a magnitude beyond a predetermined range and permits acceleration of only those electron beams having phase angles of small magnitude for generation of output energy. Furthermore, it is obvious that the scatter of energy and phase associated with said electron beam output energy is not only small but is moreover controlled within a fixed phase width and energy width. Consequently, electrons of large scatter, i.e., unstable electrons, do not emerge in the out-put.

The foregoing explanations in each case have been made with reference to the use of a drift chamber, i.e., the distance Il and l2, of a linear orbit, but as shown in FIG. 9, it is obvious that the drift chamber can assume the form of an arc, a wavy path or other geometrical shapes as may be found convenient from the standpoint of parts location, space limitations and general design considerations whereby transmitting electrons may be deected conforming to the shape of the drift chamber such as the provision of a direct current magnetic field 1S, ,as shown in the drawing. It is obvious that various changes may be made in the form, structure and arrangement of parts without departing from the spirit of the invention. Accordingly, it is not intended that the invention be limited to the specific embodiment disclosed herein primarily for purposes of illustration, rather, it is the desire to seek protection falling fairly within the scope of the appended claims. What is claimed to be new and desired to protect by Letters Patent of the United States is:

1. A charged particle accelerator apparatus comprising Va modulation gap of a first cavity followed by a drift tube with .a bunching parameter X1 in the range of 3.0-4.0 and a modulation gap of a second resonant cavity followed by a drift tube with a bunching parameter X2 in the range of 1.5-2.0 positioned in the pathway of travelV of charged particles emitted from a source of charged particles, a phase bunching means establishing a greater product of the coupling coefcient 172 and the modulation voltage V2 of the second modulation gap than the product of the coupling coeiicient 171 and modulation voltage V1 of the first modulation gap, `and an accelerator tube means for accelerating charged particles phase hunched through the medium of the aforesaid composite bunching assemblage.

2. A charged particle accelerator apparatus comprising a means for ,arcing the path of travel of charged particles emitted from `a source of charged particles a modulation gap of a first cavity followed by Ia drift tube with a bunching parameter X1 in the range of 3.0-4.0 and a second modulation gap followed by a drift tube with a bunching parameter X2 in the range of 1.5-2.0 positioned in the pathway of travel of charged particles emitted from a source of charged particles, a phase focusing means establishing a greater product of the coupling coeicient 172 and the modulation voltage V2 of the second modulation gap than the multiplied value of the coupling coeicient 171 and modulation voltage V1V of the first modulation gap, and an accelerator tube means for accelerating charged particles phase Vbunched through the medium of the aforesaid composite bunching assemblage.

3. A charged particle accelerator apparatus comprising a modulation gap of a first cavity followed by adrift tube with a bunching parameter X1 in the range of 3.0-4.0 and a modulation gap of a second cavity followed by a drift tube with la bunching parameter X2 in the range of 1.5-2.0

Vpositioned in the pathway of travel of charged particles emitted from a source of charged particles, a phase bunching means establishing a greater product of the coupling coefficient 172 and the modulation voltage V2 of the second modulation gap than the product of the coupling coefiicient 171 and modulation voltage V1 of the first modulation gap, an accelerator tube means for accelerating charged particles phase hunched through the medium of the aforesaid composite bunching assemblage, and an accelerator tube means interposed between the aforesaid phase bunch- Ving means and the light velocity accelerator tube means provided for maintaining continued acceleration of the charged particles travelling in the proximity of the velocity of light, the said acceleratortube means serving to boost the velocity of the charged particles phase bunched through the medium of the aforesaid composite bunching assemblage closer to the speed of light as well as to decrease the normalized electrical field strength a in the direction corresponding to lthe lengthwise axis of the said accelerator tube. p

References Cited UNITED STATES PATENTS 2,813,996 11/1957 Chodorow V.. 3l5-5.42 k2,922,921 l/ 1960 Nygard 3 15-5 .42 2,925,522 2/ 1960 Kelliher 3 15-5 .42 3,147,396 9/ 1964 lGeorz et al 315-142 HERMAN KARL SAALBACH, Primary Examiner. R, D. COHN, S. CHATMON, JR., Assistant Examiners, 

1. A CHARGED PARTICLE ACCELERATOR APPARATUS COMPRISING A MODULATION GAP OF A FIRST CAVITY FOLLOWED BY A DRIFT TUBE WITH A BUNCHING PARAMETER X1 IN THE RANGE OF 3.0-4.0 AND A MODULATION GAP OF A SECOND RESONANT CAVITY FOLLOWED BY A DRIFT TUBE WITH A BUNCHING PARAMETER X2 IN THE RANGE OF 1.5-2.0 POSITIONED IN THE PATHWAY OF TRAVEL OF CHARGED PARTICLES EMITTED FROM A SOURCE OF CHARGED PARTICLES, A PHASE BUNCHING MEANS ESTABLISHING A GREATER PRODUCT OF THE COUPLING COEFFICIENT N2 AND THE MODULATION VOLTAGE V2 OF THE SECOND MODULATION GAP THAN THE PRODUCT OF THE COUPLING COEFFICIENT N1 AND MODULATION VOLTAGE V1 OF THE FIRST MODULATION GAP, AND AN ACCELERATOR TUBE MEANS FOR ACCELERATING CHARGED PARTICLES PHASE BUNCHED THROUGH THE MEDIUM OF THE AFORESAID COMPOSITE BUNCHING ASSEMBLAGE. 